Multi-drug resistance (MDR) is found in a variety of human tumor cells and appears to play a significant role in the failure of cancer chemotherapy. A key to overcoming DDR is to understand how it recognizes a number of diverse compounds and actively effluxes them. Since most of these compounds are complex, making structure function analyses difficult, a series of very simple organic compounds (pyridiniums and guanidiniums) differing systematically in lipophilicity by step-wise lengthening of their alkyl chain lengths, were synthesized to study MDR. Using these compounds, a single aromatic ring and a minimal aliphatic chain length greater than 4 carbons were found to be necessary for MDR recognition. The current proposal will use these simple compounds to further define the chemical components necessary for recognition and modulation of this form of resistance. Recently, a multi-drug resistance related protein (MRP), with transport properties and resistance profiles similar to that of MDR, has been sound in human tumor samples. Preliminary evidence indicates that none of the series of simple compounds we synthesized and found to be recognized by MDR, are recognition of this new simple compound derivative. Thus, in this proposal we plan to use the simple compounds to further explore the chemical requirements for MDR recognition and distinguish them from those of MRP. These studies should provide a solid foundation for the rational design of new, and better use of known more complex compounds, to overcome thee clinically identified mechanisms of resistance. The more complex compounds will include a series of anthracycline analogs that we synthesized which differ systematically in chemical charge and lipophilicity. MDR and MRP transfectant lines are added to this proposal to confirm and further characterize our initial findings obtained with the MDR and MRP cell lines we developed by exposure to cytotoxic drugs. Growth inhibition studies and rhodamine 123 retention assays will be performed to analyze the biological functioning of these processes. Drug accumulation studies with modifiers of each of these mechanisms of resistance will be used to further investigate these processes. Photo affinity assays will complement our studies to better understand the specificities of these two mechanisms of resistance.